JP2877234B2 - Liquid level detector - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid level detection device using an optical switching device that opens and closes or changes an optical path by using the operation of a magnetic fluid. Things.

2. Description of the Related Art Conventionally, as a device for performing on / off control of a signal, an electric switch for handling an electric signal is most generally used. An electric switch usually has electric contacts for opening and closing an electric circuit, and in order to operate such electric contacts, a mechanical operation transmitting mechanism for performing operations such as rotation, sliding, and the like is required.

Further, in the field of handling optical signals, as a switching device for ON and OFF control of the optical signal,
Some devices have a structure that opens and closes an optical path using a mechanical configuration. In such a mechanical configuration, as in the case of the above-described electric switch, a mechanical operation transmission mechanism such as rotation and sliding is used.

[Problems to be Solved by the Invention] In any case, the switching device as described above must use a mechanical operation transmission mechanism in at least a part thereof. However, such mechanisms are often relatively complicated, and therefore are susceptible to failure such as breakage, and care must be taken in handling. Even if care is taken in handling, abrasion in parts performing operations such as rotation, sliding, etc. is unavoidable due to long-term use, which may cause failure.

Also, the switching device as described above has many restrictions on the environment in which it is used. For example, because of the use of mechanical motion transmission mechanisms, temperature and humidity conditions, dust, vibrations, etc. that can affect such mechanisms must be avoided. Further, in order to enhance the reliability of the electric switch, it must be used in an environment where external electric noise cannot be received. In addition, electrical switches that use electrical contacts generate sparks during operation and cannot be used in explosive atmospheres.

Therefore, an object of the present invention is to provide a liquid level detecting device using an optical switching device capable of solving the above-mentioned disadvantages of the conventional switching device.

[Means for Solving the Problems] The present invention provides a novel use of a magnetic fluid, and more specifically attempts to open or close or change an optical path using the operation of a magnetic fluid. Things.

In one aspect of the liquid level detection device according to the present invention, there is provided a liquid level detection device for detecting a liquid level of a liquid, the light source emitting light, and a magnetic fluid having a property of blocking light. A container having a concave bottom surface for receiving the magnetic fluid so that the magnetic fluid can move between a first position on the optical path and a second position off the optical path; A magnetic field generating means for generating a magnetic field that magnetically affects the magnetic fluid by supporting the magnetic field generating means so that the magnetic field generating means moves as the liquid level moves up and down. A magnetic field changing unit for forcing to take either the first position or the washing second position, a light reflecting unit disposed on the optical path, and an optical sensor disposed at an end of the optical path, It has.

Further, the container has a sealed structure made of a transparent material at least in a portion providing the optical path,
All walls of the container located on the optical path are adapted to contact the magnetic fluid when the magnetic fluid assumes the first position.

Preferably, a bottom surface of the container also serves as the light reflecting means, and the light source and the optical sensor are disposed substantially above the container.

Preferably, at least a part of the wall of the container also serves as the light reflecting means, and the light source and the light sensor are arranged at a position facing at least a part of the wall.

Furthermore, preferably, the pipe portion is accommodated so as to be fixed at a predetermined position inside the pipe member, and the pipe portion is disposed in the liquid so that the liquid does not enter the inside, and the magnetic field changing means is provided with respect to the liquid. The pipe member is provided so as to float and move along the outer peripheral surface of the pipe member.

In another aspect of the liquid level detection device according to the present invention, there is provided a liquid level detection device for detecting a liquid level of a liquid, the light source emitting light, and the light receiving surface receiving light from the light source. A magnetic fluid comprising: a container having a concave bottom surface for receiving the magnetic fluid; a magnetic field generating means for generating a magnetic field that magnetically affects the magnetic fluid; and Magnetic field changing means for supporting the magnetic field generating means so that the magnetic field generating means moves, thereby forcing the light receiving surface of the magnetic fluid to take one of a first position and a second position different from each other. When,
An optical sensor arranged to receive the reflected light from the light receiving surface when the light receiving surface takes the first position, further comprising the light source and the optical sensor located substantially above the container. Be placed.

[Operation] According to one aspect of the liquid level detection device according to the present invention,
The magnetic fluid takes either the first position or the second position by supporting the magnetic field generating means such that the magnetic field generating means moves with the vertical movement of the liquid surface by the magnetic field changing means. Is controlled as follows. When the magnetic fluid assumes the first position, the optical path is closed by the magnetic fluid because the first position is on the optical path and the magnetic fluid has the property of blocking light. On the other hand, when the magnetic fluid assumes the second position, the second position is off the optical path, so that the optical path is open.

Therefore, if an optical sensor is arranged at the end of the optical path, the output level of the optical sensor can be changed depending on the presence or absence of light received by the optical sensor. By extracting such a change in the output level, a switching operation can be achieved, and the height of the liquid level can be detected.

Further, by making the shape of the bottom surface of the container concave, the required amount of the magnetic fluid can be reduced. Furthermore, even when another magnetic field generating means that emits a magnetic field weaker than the magnetic field generating means is present outside, malfunction can be prevented beforehand when compared with a flat bottom surface of the container. Become.

Further, the container is housed so as to be fixed at a predetermined position inside the pipe member, the pipe member is arranged in the liquid so that the liquid does not enter inside, and the magnetic field changing means floats with respect to the liquid. In addition, by providing the pipe member so as to be movable along the outer peripheral surface of the pipe member, it is possible to reliably and accurately detect the liquid level.

In addition, by adopting a structure in which the bottom surface of the container also serves as the light reflecting means and the light source and the optical sensor are arranged substantially above the container, the liquid level detecting device can be reduced in size. In addition, it is also possible to adopt a structure in which at least a part of the wall of the container also serves as a light reflecting means, and a light source and an optical sensor are arranged at a position facing at least a part of the wall. It is possible to easily realize an optimum structure according to the above.

According to another aspect of the liquid level detection device according to the present invention, in a type utilizing reflection of light on the surface of a magnetic fluid, the magnetic field generating means moves as the liquid level moves up and down. By supporting the magnetic field generating means, the light receiving surface of the magnetic fluid is controlled so as to take either the first position or the second position different from each other. When the light receiving surface is in the first position, the reflected light from the light receiving surface is received by the optical sensor, while when the light receiving surface is in the second position, the reflected light from the light receiving surface is transmitted from the optical path toward the optical sensor. It comes off. Therefore, by changing the light receiving surface between the first position and the second position, the output level from the optical sensor can be changed. as a result,
In this liquid level detection device, a switching operation can be achieved by detecting such a change in the output level of the optical sensor, and the liquid level can be detected.

Further, by making the shape of the bottom surface of the container concave, the required amount of the magnetic fluid can be reduced. In addition, even when another magnetic field generating means that emits a magnetic field weaker than the magnetic field generating means is present outside, malfunction can be prevented beforehand when compared with a case where the bottom surface of the container is flat. Become. Furthermore, by adopting a structure in which the light source and the optical sensor are disposed substantially above the container, it is possible to reduce the size of the liquid level detection device.

[Effects of the Invention] As described above, according to the liquid level detection device of the present invention, by changing the externally applied magnetic field without necessarily using electricity and without using a complicated mechanical operation transmission mechanism. , The optical path can be opened and closed. Therefore, the mechanical configuration is not complicated, and there is no possibility of failure occurring in the mechanical operation mechanism.
There are almost no restrictions on the environment in which such a liquid level detection device can be used.

Further, according to the liquid level detecting device of the present invention, the device can be operated without any trouble for a long period of time. In addition, without being affected by temperature and humidity conditions, dust, etc.
A desired operation can be achieved. In addition, since no electric contact is used, it can be advantageously used as an explosion-proof liquid level detection device.

[Embodiment] FIGS. 1 and 2 show a first embodiment of the present invention.

The switching device 1 shown in these drawings includes a closed container 2, and a magnetic fluid 3 is sealed in the container 2.

The magnetic fluid 3 is composed of ferromagnetic colloid particles, a solvent and a surfactant.
For example, particles such as magnetite are used, and as a solvent in which the particles are dispersed, for example, water, kerosene, or the like is used. Some examples of magnetic fluids that can be used are shown in Taketomi and Chikaku, "Magnetic Fluids: Basics and Applications," Nikkan Kogyo Shimbun, May 23, 1988, pp. 6-7. Have been. Such a magnetic fluid 3 generally exhibits a black or brown color and has a property of blocking light when viewed optically.

It is preferable that at least the inner surface of the container 2, particularly the surface in contact with the magnetic fluid 3, is made of a material having low wettability to the magnetic fluid 3. This is for completing the movement of the magnetic fluid 3 in the container 2 quickly. Container 2 for that purpose
Is, for example, PTFE (tetrafluoroethylene resin), FEP
(Ethylene tetrafluoride-propylene hexafluoride copolymer resin)
Fluororesins, or polyolefin resins such as polypropylene and polyethylene are advantageously used. In consideration of practicality, it is preferable to use a magnetic fluid 3 using water as a solvent, and to use the container 2 made of FEP.

In this embodiment, at least the top wall 4 of the container 2 is transparent. In addition, a reflection surface is formed on the bottom surface 5 inside the container 2. Further, it is preferable that the bottom surface 5 be concave in order to minimize the required amount of the magnetic fluid 3.

A light source 6 is arranged outside the container 2, for example, above, and light emitted from the light source 6 passes through the optical fiber 7 and enters the container 2 via the transparent top wall 4.
As shown in FIG. 2, when the magnetic fluid 3 does not exist on the bottom surface 5, this incident light is reflected by the bottom surface 5, passes through the transparent top wall 4 again, and is received by another optical fiber 8. Can be Thus, an optical path 9 is formed as shown by an arrow in FIGS. 1 and 2, and an optical sensor 10 is disposed at the end of the optical path 9.

The light provided from the light source 6 may be infrared light, laser light, or the like, in addition to visible light.

On the side of the container 2, for example, a magnet movable in the vertical direction as indicated by an arrow 11, more specifically a permanent magnet 12
Is arranged. The magnet 12 is magnetized as shown by "N" and "S" in FIGS. The direction of this magnetization may be reversed. Further, it may be magnetized as shown in parentheses.

The magnet 12 functions as a magnetic field generating means for generating a magnetic field that magnetically affects the magnetic fluid 3. The container 2 also allows the magnetic fluid 3 to move between the first position shown in FIG. 1 and the second position shown in FIG. The first position is on the light path 9 and the second position is off the light path 9. The means for moving the magnet 12 in the direction indicated by the arrow 11 changes the magnetic field exerted on the magnetic fluid 3 by the magnet 12 as the magnetic field generating means, so that the magnetic fluid 3 is moved to either the first position or the second position. The magnetic field changing means for forcing to take the following is constituted.

As shown in FIG. 1, when the magnet 12 is at a position relatively distant from the container 2, the magnetic fluid 3 is at the first position on the bottom surface 5, that is, on the optical path 9, due to natural gravity.
Therefore, the optical path 9 is closed by the magnetic fluid 3 having a property of blocking light. Therefore, the light from the light source 6 does not substantially reach the optical sensor 10, and the output level of the optical sensor 10 is relatively low. Although the surface of the magnetic fluid 3 has a property of reflecting light to some extent, the amount of reflection is smaller than the amount of reflection at the bottom surface 5.
Only a little.

On the other hand, as shown in FIG. 2, when the magnet 12 approaches the container 2, the magnetic fluid 3 is attracted onto the side surface 13 of the container 2 by the magnetic field given by the magnet 12. Accordingly, the optical path 9 is opened, and the light provided from the light source 6 via the optical fiber 7 is reflected on the bottom surface 5 and then reaches the optical sensor 10 via the other optical fiber 8.
Therefore, the output level of the optical sensor 10 is relatively increased.

Thus, the output level obtained from the optical sensor 10 is changed by the movement of the magnet 12 in the direction of the arrow 11, and the switching device 1 can achieve the switching operation with the change in the output level.

The switching device 1 operates the magnet 12 artificially,
It can also be used as a switch for controlling on and off of a specific signal by such an artificial operation, and it is also possible to operate the magnet 12 in conjunction with some object so that such an object is at a predetermined position. The present invention can be applied to a switch used as a detection device that detects a signal and outputs a specific signal.

3 and 4 show an application example of the switching device 1. FIG. In this application example, the switching device 1 is used as a liquid level detection device.

The container 2 in which the magnetic fluid 3 described above is sealed is fixed at a predetermined height position in the pipe 14 whose lower end (not shown) is closed. Into the pipe 14, optical fibers 7 and 8, which constitute a part of the optical path 9, are introduced.

On the other hand, a float 15 guided by the pipe 14 so as to be movable in the vertical direction is arranged to surround the outer periphery of the pipe 14. The float 15 floats on a liquid surface (not shown) and moves up and down with the liquid surface moving up and down. The magnet 12 described above is fixed to the float 15.

As shown in FIG. 3, when the float 15 is at a relatively lower position, that is, when the liquid level does not reach the predetermined height, the magnet 12 is moved to a position relatively far from the magnetic fluid 3. Yes, giving a state corresponding to FIG. 1 described above. Therefore, the light introduced from the optical fiber 7 is blocked by the magnetic fluid 3 and does not reach the optical fiber 8.

On the other hand, as shown in FIG. 4, when the float 15 is brought to a relatively high position, that is, when the liquid level reaches a predetermined height, the magnet 12 is moved to a position close to the magnetic fluid 3. Take. This state corresponds to the state shown in FIG. 2 described above, and the light provided from the optical fiber 7 is reflected by the bottom surface 5 of the container 2 and reaches the optical fiber 8. Therefore,
A relatively high level output is obtained from the optical sensor 10 (FIG. 2), and with this output, it can be detected that the liquid level has reached a predetermined height.

In addition, the light control device according to the present invention, in the above-described application example, does not use the optical sensor 10 and directly detects the end of the optical fiber 8 by visual observation, so as to detect the liquid level. Can also be used.

The first embodiment shown in FIGS. 1 and 2 can be modified as follows. That is, as shown by the imaginary line in FIG. 2, the reflection plate 16 is disposed below the container 2. In this modification, not only the top wall 4 but also the bottom wall 17 of the container 2 are made transparent, and the light reflected on the bottom surface 5 in the first embodiment is changed to a reflecting plate.
At 16 will be reflected. In the case of this modification, the angles of the optical fiber 7 for providing the incident light and the optical fiber 8 for receiving the reflected light must be changed so as to provide an optical path passing through the reflecting plate 16, respectively. is there.

FIG. 5 shows a second embodiment of the present invention.

The embodiment shown in FIG. 5 is characterized in that an electromagnet 18 is used instead of the permanent magnet 12 as compared with the first embodiment. The direction of the magnetic field, that is, the direction of magnetization provided by the electromagnet 18 can be arbitrarily selected as shown in FIG.

The second embodiment shown in FIG. 5 is substantially the same as the first embodiment in other points. Therefore, the corresponding portions are denoted by the same reference numerals, and duplicate description will be omitted.

Even if the electromagnet 18 is fixedly provided on the side of the container 2,
Like the magnet 12 in the first embodiment, it may be provided so as to be movable in the vertical direction. When the electromagnet 18 is fixedly provided, the magnetic field changing means for changing the magnetic field exerted on the magnetic fluid 3 by the electromagnet 18 as the magnetic field generating means is realized by means such as a switch for controlling on / off of a current applied to the electromagnet 18. You.

FIG. 6 shows a third embodiment of the present invention.

In the third embodiment shown in FIG. 6, one common optical fiber 19 is used in place of the two optical fibers 7 and 8 constituting a part of the optical path 9 in the first embodiment. It is characteristic. Therefore, the optical fiber 19 transmits both the incident light and the reflected light. The other configuration is substantially the same as that of the first embodiment. Therefore, the corresponding portions are denoted by the same reference numerals, and duplicate description will be omitted.

FIGS. 7 and 8 show a fourth embodiment of the present invention.

In the fourth embodiment, the container 2 in the first embodiment is used.
A container 2a having the same shape as that described above is used, but at least one of the side walls 20 is made transparent, and an inner side surface 22 of the side wall 21 opposed to the side wall 20 is made a reflection surface.

In this embodiment, as indicated by the arrow, the light path 9a
Are formed so as to be relatively laterally oriented. That is, both ends of the optical fiber 7a for transmitting the incident light and the optical fiber 8a for transmitting the reflected light are oriented so as to relatively extend laterally from the outside of the side wall 20 toward the side wall 20. Is done.

As shown in FIG. 7, when the magnet 12a (FIG. 8) is not present near the container 2a, the magnetic fluid 3a is located on the bottom surface 5a. At this time, the magnetic fluid 3a does not block the optical path 9a, and light incident through the optical fiber 7a is reflected by the inner side surface 22 and guided to the optical sensor (not shown) by the other optical fiber 8a.

On the other hand, as shown in FIG. 8, when the magnet 12a approaches the side wall 21 of the container 2a, the magnetic fluid 3a moves onto the inner side surface 22. Therefore, light incident through the optical fiber 7a is blocked by the magnetic fluid 3a and does not reach the other optical fiber 8a.

In the above-described fourth embodiment, the position of the magnetic fluid 3a shown in FIG. 8 corresponds to the first position on the optical path 9a, while the position of the magnetic fluid 3a shown in FIG. This corresponds to a second position deviated from the optical path 9a.

FIGS. 9 and 10 show a fifth embodiment of the present invention, and FIG. 11 shows a sixth embodiment of the present invention. The fifth and sixth embodiments are different from the first to fourth embodiments in that no light reflecting means is provided on the optical path.

In the fifth embodiment shown in FIGS. 9 and 10, a container 2b having the same shape as the container 2 used in the above-described first embodiment and the like is used. The container 2b is transparent at least on the top wall 23 and the bottom wall 24. Container 2b
Inside, a magnetic fluid 3b is sealed.

In this embodiment, as is apparent from the directions and positions of the optical fibers 25 and 26, an optical path 27 penetrating the container 2b in the up-down direction is formed as shown by an arrow. One optical fiber 25 transmits incident light, and the other optical fiber 26 transmits light transmitted through the container 2b.

For example, a magnet 28 made of a permanent magnet is provided so as to be vertically movable as indicated by an arrow 29, similarly to the magnet 12 in the first embodiment described above.

As shown in FIG. 9, when the magnet 28 is at a position relatively far from the container 2b, the magnetic fluid 3b is located on the bottom wall 24. That is, the magnetic fluid 3b is located at the first position on the optical path 27. Therefore, the optical path 27 is blocked by the magnetic fluid 3b, and the incident light does not reach the optical fiber 26.

On the other hand, as shown in FIG. 10, when the magnet 28 is moved to the side of the container 2b,
The magnetic fluid 3b is moved onto the side surface 30 of the container 2b. That is, the magnetic fluid 3b is located at the second position off the optical path 27. Accordingly, the optical path 27 is opened, and the incident light provided through the optical fiber 25 passes through the container 2b, and the transmitted light reaches the other optical fiber 26. The transmitted light is provided to an optical sensor (not shown) via the optical fiber 26.

In the sixth embodiment shown in FIG. 11, a container 2c having the same shape as the container 2 used in the first embodiment and the like is used. The container 2c has at least two opposing side walls 31
And 32 are transparent. An optical fiber 25a for providing incident light is introduced on one side wall 31 and an optical fiber 26 for receiving transmitted light from the other side wall 32.
a is derived.

The state shown in FIG. 11 is a state where the magnet 28a is located on the side of the container 2c and the magnetic fluid 3c is located on both side walls 31 and 32. Therefore, the magnetic fluid 3c blocks the optical path 27a indicated by the arrow. Although illustration is omitted,
When the magnet 28a separates from the container 2c, the magnetic fluid 3c
It is located on the bottom surface 33 and opens the optical path 27a. Therefore, the transmitted light is received by the optical fiber 26a.

FIGS. 12 and 13 show a seventh embodiment of the present invention.

The seventh embodiment is characterized by the shape of the container 2d for enclosing the magnetic fluid 3d.
The first embodiment shown in FIG. 2 and FIG. 2, the second embodiment shown in FIG. 5, the third embodiment shown in FIG. 6, the fifth embodiment shown in FIG. 9 and FIG. Can be used in place of the container used in the embodiment.

The container 2d has a closed structure made of a transparent material at least in a portion providing an optical path. Then, for example, the optical path 9 shown in FIG. 2 or the optical path 27 shown in FIG. 10 is given to the container 2d, but all the walls of the container 2d located on such an optical path are , Magnetic fluid 3d
Is brought into contact with this magnetic fluid 3d when it takes the first position (FIG. 12). Therefore, an inner surface 35 protruding downward is formed on the upper surface wall 34 of the container 2d.

The seventh embodiment has the following advantages. That is, when the magnetic fluid uses water or the like as its solvent, if the container is sealed, water vapor condenses on the inner surface of the container due to an external temperature change or the like, which may fog the transparent container. is there. In this case, it is not hard to imagine adversely affecting the optical. However, as shown in FIG. 12, if the magnetic fluid 3d is configured to be in contact with all the walls located on the optical path, dew does not occur at least on the walls located on the optical path. Therefore, when the magnetic fluid 3d moves to the second position due to a change in the external magnetic field, as shown in FIG. 13, all the walls located on the optical path can be kept in a transparent state. .

FIG. 14 and FIG. 15 show an eighth embodiment of the present invention.

In the eighth embodiment, a magnetic fluid sealed in a container 36 is used.
The surface 38 of 37 is intended to be used as a light receiving surface, in other words, a reflecting surface. More specifically, the container 36
At least the upper surface wall 39 is transparent. Above the container 36, a photoelectric element 42 including a light source 40 and an optical sensor 41 is arranged. For example, a magnet 43 made of a permanent magnet
As shown by, they are provided, for example, to be movable in the vertical direction.

As shown in FIG. 14, when the magnet 43 is at a position away from the container 36, the magnetic fluid 37 has substantially no magnetic influence, and the surface 38 of the magnetic fluid 37 has a flat surface. Has formed. In this state, the incident light 45 provided from the light source 40 is reflected on the surface 38, and the reflected light 46 is
The light sensor 40 is reached.

On the other hand, as shown in FIG. 15, when the magnet 43 approaches the container 36, the magnetic fluid 37 gives
The central portion of its surface 38 is forced to sink. Therefore, the reflected light 46 reflected on the surface 38 passes through a position shifted from the optical sensor 41 and is not received by the optical sensor 41.

In this manner, the output level of the optical sensor 41 can be changed, thereby realizing a switching device that performs a switching operation.

As described above, the present invention has been described with reference to various illustrated embodiments, but various other modifications are possible within the scope of the present invention.

For example, although the electromagnet 18 is disclosed in the second embodiment shown in FIG. 5, such an electromagnet can be used in place of the magnet used in other embodiments.

Further, when the solvent contained in the magnetic fluid is volatile, it is preferable that the container for enclosing the solvent has a sealed structure, but when such a solvent is not volatile or has only low volatility. Alternatively, the container may be of an open construction.

[Brief description of the drawings]

FIG. 1 and FIG. 2 are views showing a first embodiment of the present invention, in which different operation states are shown. FIG. 3 and FIG. 4 are cross-sectional views illustrating a case where the first embodiment is used as a liquid level detecting device, and show different operation states from each other. FIG. 5 is a diagram showing a second embodiment of the present invention. FIG. 6 is a diagram showing a third embodiment of the present invention. 7 and 8 are views showing a fourth embodiment of the present invention, and show different operation states from each other. FIG. 9 and FIG. 10 are views showing a fifth embodiment of the present invention, and show different operation states from each other. FIG. 11 is a view showing a sixth embodiment of the present invention. FIG. 12 and FIG. 13 are views showing a seventh embodiment of the present invention, and show different operation states from each other. FIG. 14 and FIG. 15 are views showing an eighth embodiment of the present invention, and show different operation states from each other. In the figure, 1 is a switching device, 2, 2a, 2b, 2c, 2d, 36
Is a container, 3, 3a, 3b, 3c, 3d, 37 is a magnetic fluid, 6, 40 is a light source, 9,
9a, 27, 27a are optical paths, 10, 41 are optical sensors, 12, 12a, 28, 28a, 43
Is a magnet (magnetic field generating means), 11, 29, and 44 are arrows (magnetic field changing means) indicating the moving direction of the magnet, and 18 is an electromagnet (magnetic field generating means and magnetic field changing means).

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G02B 26/02 G01F 23/00

Claims (5)

(57) [Claims] 1. A liquid level detecting device for detecting the level of a liquid surface of a liquid, comprising: a light source that emits light; a magnetic fluid having a property of blocking light; A container having a concave bottom surface for receiving the magnetic fluid so as to be movable between a position 1 and a second position deviated from the optical path; and generating a magnetic field magnetically affecting the magnetic fluid. Magnetic field generating means for supporting the magnetic field generating means so that the magnetic field generating means moves with the vertical movement of the liquid surface, so that the magnetic fluid is in the first position or the second position. A magnetic field changing unit for forcing to take any one of the positions, a light reflecting unit disposed on the optical path, and an optical sensor disposed at an end of the optical path, wherein the container has at least the optical path. From transparent material in the part to give Wherein all walls of the container located on the optical path are adapted to contact the magnetic fluid when the magnetic fluid assumes the first position. Surface detection device. 2. The liquid level detecting device according to claim 1, wherein a bottom surface of said container also serves as said light reflecting means, and said light source and said optical sensor are disposed substantially above said container. 3. The light source and the light sensor are arranged at a position where at least a part of a wall of the container also serves as the light reflecting means, and at least a part of the wall is opposed to at least a part of the wall. 2. The liquid level detecting device according to 1. 4. The container is housed so as to be fixed at a predetermined position inside a pipe member, wherein the pipe member is arranged in the liquid so that the liquid does not enter the inside, and the magnetic field changing means is provided in the pipe member. The liquid level detecting device according to any one of claims 1 to 3, wherein the liquid level detecting device is provided so as to float on the liquid and move along the outer peripheral surface of the pipe member. 5. A liquid level detecting device for detecting a liquid level of a liquid, comprising: a light source that emits light; a magnetic fluid having a light receiving surface that receives light from the light source; A container having a concave receiving bottom surface, magnetic field generating means for generating a magnetic field that magnetically influences the magnetic fluid, and the magnetic field generating means moving as the liquid level moves up and down. By supporting the magnetic field generating means, the magnetic field changing means for forcing the light receiving surface of the magnetic fluid to take one of a first position and a second position different from each other, and the reflected light from the light receiving surface A light sensor disposed so as to be able to receive the light receiving surface when the light receiving surface takes the first position, wherein the light source and the light sensor are disposed substantially above the container. .